Valves that feature bodies machined from either hot or cold drawn metal bar, having either circular cross sections or sections formed as regular polygons are commonly referred to as “bar stock” valves. Bar stock valve bodies are particularly amenable to production on high speed automatic machines and therefore offer economies in manufacture not enjoyed by manufacturers of cast and forged valves.
Traditional bar stock valve bodies place the flow passage substantially along the central axis of the bar. The starting bar size is based on the resulting wall thickness, following machining, necessary to withstand the operating pressures the valve is exposed to in service. Choice of end connection also plays a role in sizing initial bar stock size. The bar size used, however, often is overly sufficient for the wall thickness requirements of the valve.
This over-design of the valve body frequently results from the need to provide adequate valve stem bearing support and adequate space for stem seals. To accommodate these items, the valve designer often selects a larger bar size, resulting in increased overall weight and cost of the valve body. Due to the manufacturing techniques used, it is inefficient to place the additionally required material locally in the valve body only where needed.
The over-design becomes more pronounced if an additional (third) port is to be added to a bar stock valve body. The third port typically is located on the opposite valve body side from the stem, decreasing further the possibility of obtaining sufficient space for the stem bearing support and seals.